TSTyche

The Essential Type Testing Tool.

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TSTyche is a type testing tool for TypeScript. It ships with describe() and test() helpers, expect style assertions and a mighty test runner.

Helpers

If you are used to test JavaScript, a simple type test file should look familiar:

1import { expect, test } from "tstyche";
2
3function firstItem<T>(target: Array<T>): T | undefined {
4  return target[0];
5}
6
7test("firstItem", () => {
8  expect(firstItem(["a", "b", "c"])).type.toBe<string | undefined>();
9
10  expect(firstItem()).type.toRaiseError("Expected 1 argument");
11});

To organize, debug and plan tests TSTyche has:

• test(), it() and describe() helpers,
• with .only, .skip and .todo run mode flags.

Assertions

The assertions can be used to write type tests (like in the above example) or mixed in your functional tests:

1import assert from "node:assert";
2import test from "node:test";
3import * as tstyche from "tstyche";
4
5function secondItem<T>(target: Array<T>): T | undefined {
6  return target[1];
7}
8
9test("handles numbers", () => {
10  assert.strictEqual(secondItem([1, 2, 3]), 2);
11
12  tstyche.expect(secondItem([1, 2, 3])).type.toBe<number | undefined>();
13});

Here is the list of all matchers:

• .toBe(), .toBeAssignableTo(), .toBeAssignableWith() compare types or types of expression,
• .toAcceptProps() checks JSX component props type,
• .toHaveProperty() looks up keys on an object type,
• .toRaiseError() captures the type error message or code,
• .toBeString(), .toBeNumber(), .toBeVoid() and 9 more shorthand checks for primitive types.

Runner

The tstyche command is the heart of TSTyche. For example, it can select test files by path, filter tests by name and pass them through a range of TypeScript versions:

1tstyche query-params --only multiple --target '>=5.0 <5.3'

This simple! (And it has watch mode too.)

Documentation

Visit https://tstyche.org to view the full documentation.

Feedback

If you have any questions or suggestions, start a discussion or open an issue on GitHub. Preferring a chat? Join our Discord server.

License

MIT © TSTyche